The Dare That Led to the Devil (Black Butler Fanfic)

((Formally The Curse of His Bite))
Heaven and Hell have lived side by side for centuries upon centuries, coexisting but never getting along. However, two rules keeps both sides safe: One. Never cross the border. Two. Never steal from the other side. If you are caught breaking either of these rules, the Demon or Angel who caught you ultimately decides your fate.
Katarina knew these rules, and she has always followed them... Up until now. On a dare, she crosses the border to retrieve proof that she ventured into the dark pits of Hell... All while not flying. Being one of the fastest flyers around, it was understandable that she it was against the rules for her to fly, but running through Hell when others can sense you are a holy being... Not so easily done.
So, what can Katarina do when she injures herself during said challenge and one of the oldest Outcasts literally catches her in the act of both stealing and crossing the border? What can she think when said Outcast turns out to be the very ruler of Hell itself?
What does this stunningly handsome Demon King have in store for her? Can she make it out alive... and unmarked?
She could only pray to the God she would one day serve.